Electrochemical production of an alkaline solution using CO2

ABSTRACT

An electrochemical system comprising a cathode electrolyte comprising added carbon dioxide and contacting a cathode; and a first cation exchange membrane separating the cathode electrolyte from an anode electrolyte contacting an anode; and an electrochemical method comprising adding carbon dioxide into a cathode electrolyte separated from an anode electrolyte by a first cation exchange membrane; and producing an alkaline solution in the cathode electrolyte and an acid.

CROSS-REFERENCE

This application is a continuation-in-part of, and claims priority to,U.S. patent application Ser. No. 12/541,055 filed on Aug. 13, 2009,titled “Gas Diffusion Anode and CO₂ Cathode Electrolyte System” which isa continuation-in-part of U.S. patent application Ser. No. 12/503,557filed on Jul. 15, 2009, titled: “CO2 Utilization In ElectrochemicalSystems”, both of which are herein incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

In many chemical processes an alkaline solution is required to achieve achemical reaction, e.g., to neutralize an acid, or buffer the pH of asolution, or precipitate an insoluble hydroxide and/or carbonate and/orbicarbonate from a solution. One method by which the alkaline solutionis produced is by an electrochemical system as disclosed in theabove-referenced US patent applications, herein incorporated byreference in their entirety. In producing an alkaline solutionelectrochemically, a large amount of energy, salt and water may be used;consequently, lowering the energy and material used is highly desired.An alkaline solution includes a solution comprising hydroxide ions,and/or carbonate ions, and/or bicarbonate ions.

SUMMARY OF THE INVENTION

In one embodiment, this invention pertains to an electrochemical systemcomprising a cathode electrolyte comprising added carbon dioxide, andcontacting a cathode; and a first cation exchange membrane separatingthe cathode electrolyte from an anode electrolyte contacting an anode.In another embodiment, the invention pertains to an electrochemicalmethod comprising adding carbon dioxide into a cathode electrolyteseparated from an anode electrolyte by a first cation exchange membrane;and producing an alkaline solution in the cathode electrolyte withoutproducing a gas at the anode in contact with the anode electrolyte. Inanother embodiment, the invention pertains to a method comprisingproducing an acid in an electrochemical system comprising added carbondioxide in the cathode electrolyte; and contacting a mineral with theacid.

In some embodiments, the system comprises a second cation exchangemembrane contacting the anode electrolyte; the carbon dioxide iscontained in a waste gas; the waste gas comprises emissions from anelectrical power generating plant, a cement plant, an ore processingfacility or a fermentation system; atmospheric carbon dioxide isexcluded from the cathode electrolyte; the cathode electrolyte isoperatively connected to the industrial facility; the pH of the cathodeelectrolyte is 7 and above; the pH of the cathode electrolyte is between7 and 14; the pH of the cathode electrolyte is between 7 and 9; the pHof the cathode electrolyte is between 8 and 11; the pH of the anodeelectrolyte is less than 7; the pH of the anode electrolyte is less than4; the cathode electrolyte comprises hydroxide ions and/or bicarbonateions and/or carbonate ions; the cathode electrolyte comprises sodiumions; the cathode electrolyte is operatively connected to a carbonateand/or bicarbonate precipitator; the carbonates and/or bicarbonatescomprise calcium and/or magnesium; hydrogen is oxidized at the anode;the cathode is configured to produce hydrogen gas; a gas delivery systemis configured to direct hydrogen gas from the cathode to the anode; theanode electrolyte comprises an acid and a salt solution; the saltsolution comprises sodium ions and chloride ions; the system isconfigured to produce hydrogen ions at the anode with less than 1Vacross the anode and cathode, without producing a gas at the anode; thesystem is configured to migrate hydrogen ions into the anodeelectrolyte; the system is configured to produce hydroxide ions at thecathode; the system is configured to migrate hydroxide ions into thecathode electrolyte; the system is configured to migrate cations fromthe anode electrolyte into the cathode electrolyte; the cations comprisesodium ions; the anode electrolyte is operatively connected to a mineraldissolution system configured to dissolve minerals; the mineral solutioncomprises calcium ions and/or magnesium ions; the minerals comprisesmafic minerals; the mineral dissolution system is operatively connectedto a separator configured to separate sodium ions and chloride ions fromthe mineral solution; a concentrator is configured to concentrate sodiumions and chloride ions into a salt solution.

In some embodiments, the method comprises applying a voltage across thecathode in contact with the cathode electrolyte and the anode in contactwith the anode electrolyte, wherein a gas is not produced at the anode;and wherein the voltage is less than 1V; and wherein the anode comprisesa second cation exchange membrane contacting the anode electrolyte. Insome embodiments, the method comprises producing hydroxide ions and/orbicarbonate ions and/or carbonate ions in the cathode electrolyte;wherein the carbon dioxide is contained in a waste gas, e.g., anindustrial waste gas; wherein the waste gas is emitted from anindustrial plant; wherein the industrial plant comprises an electricalpower generating plant, a cement production plant or an ore processingfacility and the like; wherein carbon dioxide in ambient air is excludedfrom the cathode electrolyte. In some embodiments, the method comprisesmaintaining a pH of 7 or greater in the cathode electrolyte; maintaininga pH of between 7 and 9 in the cathode electrolyte; maintaining a pH ofbetween 8 and 11 in the cathode electrolyte; maintaining a pH of lessthan 7 in the anode electrolyte; maintaining a pH of less than 4 in theanode electrolyte; oxidizing hydrogen gas at the anode to producehydrogen ions; migrating the hydrogen ions through the second cationexchange membrane into the anode electrolyte; producing hydroxide ionsand hydrogen gas at the cathode and migrating hydroxide ions into thecathode electrolyte; directing hydrogen gas from the cathode to theanode; migrating cations ions through the first cation exchange membraneinto the cathode electrolyte, wherein the cations comprise sodium ions;and producing an acid in the anode electrolyte.

In some embodiments, the method comprises producing an acid in the anodeelectrolyte, without generating a gas at the anode; oxidizing hydrogengas at the anode; wherein the acid produced comprises hydrochloric acid;producing hydrogen gas at the cathode; producing an alkaline solution inthe cathode electrolyte; migrating sodium ions into the cathodeelectrolyte; wherein the alkaline solution comprises sodium hydroxide,sodium bicarbonate and/or sodium carbonate; the voltage is less than 1V;the anode electrolyte is separated from the cathode electrolyte by firstcation exchange membrane; the anode comprises a second cation exchangemembrane in contact with the anode electrolyte; the anode electrolytecomprises a salt; the salt comprises sodium chloride. In someembodiments, the method comprises dissolving a mineral with the acid toproduce a mineral solution; producing calcium ions and/or magnesiumions; the mineral comprises a mafic mineral; and the mineral solution isfiltered to produce a filtrate comprising sodium ions and chloride ionssolution. In other embodiments, the method includes; concentrating thefiltrate to produce a salt solution; utilizing the salt solution as theanode electrolyte; precipitating a carbonate and/or bicarbonate with thecathode electrolyte, wherein the carbonate and/or bicarbonate comprisescalcium and/or magnesium carbonate and/or bicarbonate.

Accordingly, with the system and method, by selectively placing ionexchange membranes, e.g., cation exchange membranes, between the anodeelectrolyte and the cathode electrolyte; and by controlling the voltageacross the anode and cathode, e.g., maintaining less than 2V; and bycontrolling the pH of the cathode electrolyte and/or the anodeelectrolyte; and by oxidizing hydrogen gas at the anode withoutproducing a gas at the anode, an alkaline solution comprising hydroxideions and/or carbonate ions and/or bicarbonate ions is produced in thecathode electrolyte; hydrogen gas is produced at the cathode; hydrogenions are produced at the anode from hydrogen gas supplied to the anode,without producing a gas at the anode, and hydrogen ions are migratedinto an electrolyte, e.g., the anode electrolyte, to produce an acid inthe anode electrolyte. In various embodiments, utilizing hydrogen gas atthe anode from hydrogen generated at the cathode, eliminates the needfor an external supply of hydrogen; consequently, the overallutilization of energy by the system to produce the alkaline solution isreduced.

In some embodiments, the alkaline solution produced is utilized tosequester carbon dioxide, e.g., from industrial waste gases, intocementitous carbonate materials as disclosed, for example, in U.S.patent application Ser. No. 12/126,776 filed on May 23, 2008 and titled“Hydraulic Cements Comprising Carbonate Compound Compositions”, hereinincorporated by reference in its entirety.

Advantageously, with the present system and method, since a relativelylow voltage is utilized across the anode and cathode to produce thealkaline solution, and since hydrogen generated at the cathode isutilized at the anode, a relatively low amount of energy is utilized toproduce the alkaline solution. Also, by the system and method, sincecarbon dioxide from industrial waste gases is utilized to produce thealkaline solution, the system and method can be utilized to sequesterlarge amounts of carbon dioxide and thus reduce carbon dioxide emissionsinto the atmosphere. Further, the acid produced can be utilized invarious ways including dissolving materials, e.g., minerals and biomass.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings illustrate by way of examples and not bylimitation some embodiments of the present system and method.

FIG. 1 is an illustration of an embodiment of the present system.

FIG. 2 is an illustration of an embodiment of the anode portion of thesystem.

FIG. 3 is a flow chart of an embodiment of the method.

FIG. 4 is an illustration of an embodiment of the system.

FIG. 5 is an illustration of the carbonate/bicarbonate ion speciation inH₂O v. the pH of the solution at 25° C.

FIG. 6 is an illustration of a voltage difference across the anode andcathode v. pH of the cathode electrolyte in an embodiment of the system.

FIG. 7 is an illustration of an embodiment of the system.

FIG. 8 is an illustration of an embodiment of the system.

FIG. 9 is an illustration of an embodiment of the system.

FIG. 10 is a flow chart of an embodiment of the method.

FIG. 11 is a flow chart of an embodiment of the method.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides systems and methods for an electrochemicalproduction of an alkaline solution in a cathode electrolyte and an acidin an electrolyte, e.g., the anode electrolyte. In various embodiments,carbon dioxide is added to the cathode electrolyte and a gas is notproduced at the anode; in various embodiments, an alkaline solutioncomprising, e.g., sodium hydroxide and/or sodium carbonate and/or sodiumbicarbonate is produced in the cathode electrolyte. In variousembodiments, a salt solution comprising, e.g., sodium chloride, is usedas the anode electrolyte to produce the alkaline solution. Also, asdescribed herein, an acid solution, e.g., hydrochloric acid, is producedin the anode electrolyte by hydrogen ions migrating from the anode intothe anode electrolyte, and with cations, e.g., chloride ions, present inthe anode electrolyte.

In some embodiments, the acid solution produced is utilized to dissolvea mineral, e.g., serpentine or olivine, to obtain a divalent cationsolution, e.g., calcium and magnesium ion solution, which may in someembodiments be used with the alkaline solution to precipitate carbonatesand/or bicarbonates derived from carbon dioxide in a waste gas stream,e.g., carbon dioxide in the exhaust gases of a fossil fuelled powergenerating plant or a cement producing plant. In some embodiments, asodium chloride solution is used as the anode electrolyte.

Also, as disclosed herein, on applying a voltage across the anode andcathode, cations, e.g., sodium ions in the anode electrolyte, migratefrom the anode electrolyte through the first cation exchange membraneinto the cathode electrolyte to produce an alkaline solution comprising,sodium hydroxide and/or sodium carbonate and/or sodium bicarbonate inthe cathode electrolyte; and anions in the anode electrolyte, e.g.,chloride ions, and hydrogen ions migrated from the anode to produce anacid, e.g., hydrochloric acid in the anode electrolyte.

Further, as described herein, hydrogen gas and hydroxide ions areproduced at the cathode, and in some embodiments, some or all of thehydrogen gas produced at the cathode is directed to the anode where itis oxidized to produce hydrogen ions.

However, as can be appreciated by one ordinarily skilled in the art,since the present system and method can be configured with analternative, equivalent salt solution in the anode electrolyte, e.g., apotassium sulfate solution, to produce an equivalent alkaline solution,e.g., potassium hydroxide and/or potassium carbonate and/or potassiumbicarbonate in the cathode electrolyte, and an equivalent acid, e.g.,sulfuric acid in the anode electrolyte, by applying the voltage asdisclosed herein across the anode and cathode, the invention is notlimited to the exemplary embodiments described herein, but is adaptablefor use with an equivalent salt solution, e.g., potassium sulfate, toproduce an alkaline solution in the cathode electrolyte, e.g., potassiumcarbonate and/or potassium bicarbonate and an acid, e.g., sulfuric acidin the anode electrolyte.

Accordingly, to the extent that such equivalents are based on orsuggested by the present system and method, these equivalents are withinthe scope of the appended claims.

With reference to FIG. 7, in one embodiment, the system 700 comprises acathode 106 in contact with a cathode electrolyte 108 comprising addedcarbon dioxide 107, wherein the cathode electrolyte is separated from ananode electrolyte 104 by first cation exchange membrane 116. In anembodiment as is illustrated in FIG. 8, the system 800 comprises ananode 102 that is separated from the anode electrolyte by a secondcation exchange membrane 122 that is in contact with the anode 102.

In systems 700, 800 as illustrated in FIGS. 7 and 8, the first cationexchange membrane 116 is located between the cathode 106 and anode 102such it separates the cathode electrolyte 108 from the anode electrolyte104. Thus as is illustrated in FIGS. 7 and 8, on applying a relativelylow voltage, e.g., less than 2V or less than 1V, across the anode 102and cathode 106, hydroxide ions (OH⁻) and hydrogen gas (H₂) are producedat the cathode 106, and hydrogen gas is oxidized at the anode 102 toproduce hydrogen ions at the anode 102, without producing a gas at theanode. In certain embodiments, the hydrogen gas produced at the cathodeis directed to the anode through a hydrogen gas delivery system 112, andis oxidized to hydrogen ions at the anode. In various embodiments,utilizing hydrogen gas at the anode from hydrogen generated at thecathode, eliminates the need for an external supply of hydrogen;consequently, the utilization of energy by the system to produce thealkaline solution is reduced.

In certain embodiments as illustrated in FIGS. 7 and 8, under theapplied voltage 114 across the anode 102 and cathode 106, hydroxide ionsare produced at the cathode 106 and migrate into the cathode electrolyte108, and hydrogen gas is produced at the cathode. In certainembodiments, the hydrogen gas produced at the cathode 106 is collectedand directed to the anode, e.g., by a hydrogen gas delivery system 122,where it is oxidized to produce hydrogen ions at the anode. Also, asillustrated in FIGS. 7 and 8, under the applied voltage 114 across theanode 102 and cathode 106, hydrogen ions produced at the anode 102migrate from the anode 102 into the anode electrolyte 104 to produce anacid, e.g., hydrochloric acid.

In certain embodiments, the first cation exchange membrane 116 isselected to allow passage of cations therethrough while restrictingpassage of anions therethrough. Thus, as is illustrated in FIGS. 7 and8, on applying the low voltage across the anode 102 and cathode 106,cations in the anode electrolyte 104, e.g., sodium ions in the anodeelectrolyte comprising sodium chloride, migrate into the cathodeelectrolyte through the first cation exchange membrane 116, while anionsin the cathode electrolyte 108, e.g., hydroxide ions, and/or carbonateions, and/or bicarbonate ions, are prevented from migrating from thecathode electrolyte through the first cation exchange membrane 116 andinto the anode electrolyte 104.

Thus, as is illustrated in FIGS. 7 and 8, where the anode electrolyte104 comprises an aqueous salt solution such as sodium chloride in water,a solution, e.g., and alkaline solution, is produced in the cathodeelectrolyte 108 comprising cations, e.g., sodium ions, that migrate fromthe anode electrolyte 104, and anions, e.g., hydroxide ions produced atthe cathode 106, and/or carbonate ions and or bicarbonate ions producedby dissolving carbon dioxide 107 in the cathode electrolyte.

Concurrently, in the anode electrolyte 104, an acid, e.g., hydrochloricacid is produced from hydrogen ions migrating from the anode 102 andanions, e.g., chloride ions, present from the anode electrolyte.

With reference to FIG. 8, an anode comprising a second cation exchangemembrane 122 is utilized to separate the anode 102 from the anodeelectrolyte 104 such that on a first surface, the cation exchangemembrane 122 is in contact with the anode 102, and an opposed secondsurface it is in contact with the anode electrode electrolyte 104. Thus,as can be appreciated, in this embodiment, since the second cationexchange membrane is permeable to cations, e.g., hydrogen ions, theanode is in electrical contact with the anode electrolyte through thesecond cation exchange membrane. In some embodiments, the anode asillustrated in FIG. 8 may comprise a gas diffusion anode as describedbelow.

Thus, in the embodiment of FIG. 8, as with the embodiment illustrated inFIG. 7, on applying the low voltage across the anode 102 and cathode106, hydrogen ions produced at the anode 102 from oxidation of hydrogengas at the anode migrate through the second cation exchange membrane 122into the anode electrolyte 104. At the same time, cations in the anodeelectrolyte, e.g., sodium ions in the anode electrolyte comprisingsodium chloride, migrate from the anode electrolyte 104 into the cathodeelectrolyte 108 through the first cation exchange membrane 116, whileanions in the cathode electrolyte 108, e.g., hydroxide ions, and/orcarbonate ions, and/or bicarbonate ions, are prevented from migratingfrom the cathode electrolyte 108 to the anode electrolyte 104 throughthe first cation exchange membrane 116.

Also, in the embodiment as illustrated in FIG. 8, hydrogen ionsmigrating from the anode 102 through the second cation exchange membrane122 into the anode electrolyte 104 will produce an acid, e.g.,hydrochloric acid with the cations, e.g., chloride ions, present in theanode electrolyte; and in the cathode electrolyte 108, an alkalinesolution is produce from cations present in the cathode electrolyte andanions, e.g., sodium ions, that migrate from the anode to the cathodeelectrolyte through the first cation exchange membrane 116.

In some embodiments, cation exchange membranes 116 and 122 areconventional and are available from, for example, Asahi Kasei of Tokyo,Japan; or from Membrane International of Glen Rock, N.J., or DuPont, inthe USA. However, it will be appreciated that in some embodiments,depending on the need to restrict or allow migration of a specificcation or an anion species between the electrolytes, a cation exchangemembrane that is more restrictive and thus allows migration of onespecies of cations while restricting the migration of another species ofcations may be used as, e.g., a cation exchange membrane that allowsmigration of sodium ions into the cathode electrolyte from the anodeelectrolyte while restricting migration of hydrogen ions from the anodeelectrolyte into the cathode electrolyte, may be used. Such restrictivecation exchange membranes are commercially available and can be selectedby one ordinarily skilled in the art.

As is illustrated in FIG. 8, the anode 102 comprises a second cationexchange membrane 112 that separates the anode 102 from the anodeelectrolyte 104 and is attached to the anode. Thus, in some embodiments,the anode and second cation exchange membrane may comprise an integralgas diffusion anode that is commercially available, or can be fabricatedas described for example in commonly assigned U.S. Provisional PatentApplication No. 61/151,484, titled “Electro-catalyst Electrodes forLow-voltage electrochemical Hydroxide System”, filed Feb. 10, 2009,herein fully incorporated by reference. However, as can be appreciatedby one ordinarily skilled in the art, notwithstanding that a gasdiffusion anode is illustrated and utilized in FIGS. 7 and 8 anddescribed herein, in the some embodiments, any conventional anode thatcan be configured to oxidize hydrogen gas to produce hydrogen ions asdescribed herein can be utilized.

With reference to FIGS. 7 and 8, in some embodiments, the cathodeelectrolyte 108 is operatively connected to a supply of carbon dioxidegas 107, contained, e.g., in an industrial plant, e.g., a powergenerating plant, a cement plant, or an ore smelting plant. Ifnecessary, this source of carbon dioxide comprises a gas wherein theconcentration of carbon dioxide is greater than the concentration ofcarbon dioxide in the ambient atmosphere. This source of carbon dioxidemay also contain other gaseous and non-gaseous components of acombustion process, e.g., nitrogen gas, SO_(X), NO_(X), as is describedin commonly assigned U.S. Provisional Patent application No. 61/223,657,titled “Gas, Liquids, Solids Contacting Methods and Apparatus”, filedJul. 7, 2009 herein fully incorporated by reference. However, as can beappreciated, this source of carbon dioxide can be cleaned and utilizedas the carbon dioxide added to the cathode electrolyte 108.

Although carbon dioxide is present in ordinary ambient air, in view ofits very low concentration, ambient carbon dioxide may not providesufficient carbon dioxide to achieve the results obtained with thepresent system and method that utilize carbon dioxide taken from anindustrial waste gas steam, e.g., from the stack gases of a fossilfuelled power generating plant or a cement production plant. Also, insome embodiments of the system and method, since the cathode electrolyteis contained in closed system wherein the pressure of the added carbondioxide gas within the system is greater than the ambient atmosphericpressure, ambient air and hence ambient carbon dioxide is typicallyprevented from infiltrating into the cathode electrolyte.

In some embodiments, and with reference to FIGS. 5-8, carbon dioxide isadded to the cathode electrolyte to dissolve and produce carbonic acidthat dissociates to hydrogen ions and carbonate ions and/or bicarbonateions, depending on the pH of the cathode electrolyte. Concurrently, asdescribed above, hydroxide ions, produced from electrolyzing water inthe cathode electrolyte, may react with the hydrogen ions to producewater in the cathode electrolyte. Thus, depending on the degree ofalkalinity desired in the cathode electrolyte, the pH of the cathodeelectrolyte may be adjusted and in some embodiments is maintainedbetween and 7 and 14 or greater; or between 7 and 9; or between 8 and 11as is well understood in the art, and as illustrated in carbonatespeciation diagram of FIG. 5. In some embodiments, the pH of the cathodeelectrolyte may be adjusted to any value between 7 and 14 or greater,including a pH 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5,12.0, 12.5, 13.0, 13.5, 14.0 and greater.

Similarly, in some embodiments of the system, the pH of the anodeelectrolyte is adjusted and is maintained between less than 0 and up to7 and/or between less than 0 and up to 4, by regulating theconcentration of hydrogen ions that migrate into the anode electrolytefrom oxidation of hydrogen gas at the anode, and/or the withdrawal andreplenishment of anode electrolyte in the system. In this regard and ascan be appreciated by one ordinarily skilled in the art and withreference to FIG. 6, since the voltage across the anode and cathode isdependent on several factors including the difference in pH between theanode electrolyte and the cathode electrolyte as can be determined bythe Nerst equation, in some embodiments, the pH of the anode electrolyteis adjusted to a value between 0 and 7, including 0, 0.5, 1.0, 1.5, 2.0,2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 and 7, depending on thedesired operating voltage across the anode and cathode. Thus, as can beappreciated, in equivalent systems, where it is desired to reduce theenergy used and/or the voltage across the anode and cathode, e.g., as inthe Chloralkali process, carbon dioxide can be added to the electrolyteas disclosed herein to achieve a desired pH difference between the anodeelectrolyte and cathode electrolyte. Thus, to the extent that suchsystems utilize carbon dioxide, these equivalent systems are within thescope of the present invention.

With reference to FIGS. 7 and 8, in some embodiments, the anodeelectrolyte 102 comprises a salt solution that includes sodium ions andchloride ions; the system 700, 800 is configured to produce the alkalinesolution in the cathode electrolyte 108 while also producing hydrogenions at the anode 106, with less than 1V across the anode 122 andcathode 106, without producing a gas at the anode; the system 700, 800is configured to migrate hydrogen ions from the anode into the anodeelectrolyte; the anode electrolyte comprises an acid; the system 700,800 is configured to produce bicarbonate ions and/or carbonate ions inthe cathode electrolyte 108; migrate hydroxide ions from the cathode 106into the cathode electrolyte; migrate cations, e.g., sodium ions, fromthe anode electrolyte 104 into the cathode electrolyte through the firstcation exchange membrane 116; hydrogen gas is provided to the anode; anda hydrogen gas delivery system 112 is configured to direct hydrogen gasfrom the cathode to the anode.

With reference to FIGS. 7-9, in some embodiments the cathode electrolyte108 may be operatively connected to a system for further processing ofthe cathode electrolyte, e.g., a carbonate and/or bicarbonateprecipitating system 912 comprising a precipitator configured toprecipitate carbonates and/or bicarbonates from a solution, wherein insome embodiments the carbonates and/or bicarbonates comprise calciumand/or magnesium carbonate and/or bicarbonate. Also as illustrated inFIG. 9, in some embodiments, the anode electrolyte 104 comprising anacid, e.g., hydrochloric acid, and a depleted salt solution comprisinglow amount sodium ions, is operatively connected to a system for furtherprocessing of an acid, e.g., a mineral dissolution system 904 that isconfigured to dissolve minerals and produce a mineral solutioncomprising calcium ions and/or magnesium ions, e.g., mafic minerals suchas olivine and serpentine. In some embodiments, not shown in FIG. 9, theacid may used for other purposes in addition to or instead of mineraldissolution. Such use includes use as a reactant in production ofcellulosic biofules, use the production of polyvinyl chloride (PVC), andthe like. System appropriate to such uses may be operatively connectedto the electrochemistry unit, or the acid may be transported to theappropriate site for use.

In the some embodiments, the mineral dissolution system 904 isoperatively connected to nano-filtration system 910 that is configuredto separate sodium ions and chloride ions from the mineral solutioncomprising, e.g., calcium ions, magnesium ions, silica, hydrochloricacid and/or sodium hydroxide. In some embodiments, the nano-filtrationsystem 910 is configured with a reverse osmosis system 914 that iscapable of concentrating sodium ions and chloride ions into a saltsolution that is used as the anode electrolyte 104.

With reference to FIGS. 1-10, the method 1000 in some embodimentscomprises a step 1002 of adding carbon dioxide into a cathodeelectrolyte 108 in contact with a cathode 106 wherein the cathodeelectrolyte is separated from an anode electrolyte 104 by a first cationexchange membrane 116; and producing an alkaline solution in the cathodeelectrolyte by applying a voltage 114 of less that 1V across the cathode106 and an anode 102 in contact with the anode electrolyte withoutproducing a gas at the anode.

In some embodiments of the method 1000, the anode 102 is in contact witha second cation exchange membrane 122 that separates the anode from theanode electrolyte; the alkaline solution 108 comprises hydroxide ionsand/or bicarbonate ions and/or carbonate ions; the carbon dioxide 107 iscontained in wastes gases of an industrial plant, e.g., an electricalpower generating plant, a cement production plant, a fermentationprocess or an ore processing facility.

In some embodiments, by the method 1000, ambient air is excluded thecathode electrolyte 108; a pH of between and 7 and 14 or greater usmaintained in the cathode electrolyte; a pH of between 7 and 9 ismaintained in the cathode electrolyte; a pH of between 8 and 11 ismaintained in the cathode electrolyte; a pH of from less than 0 and upto 7 is maintained in the anode electrolyte; a pH of from less than 0and up to 4 is maintained in the anode electrolyte; hydrogen gas isoxidized at the anode 102 to produce hydrogen ions and hydrogen ions aremigrated from the anode through the second cation exchange membrane 122into the anode electrolyte; hydroxide ions and hydrogen gas are producedat the cathode 106; hydroxide ions are migrated from the cathode 106into the cathode electrolyte 108; hydrogen gas is directed from thecathode 106 to the anode 102; cations ions are migrated from the anodeelectrolyte 104 through the first cation exchange membrane 122 into thecathode electrolyte 108 wherein the cations comprise sodium ions.

In some embodiments, the method 1000 comprises producing sodiumhydroxide and/or sodium carbonate ions and/or sodium bicarbonate ions inthe cathode electrolyte 108; producing an acid and a depleted saltsolution in the anode electrolyte 104 comprising sodium ions andchloride ions; utilizing the anode electrolyte to dissolve minerals 904and produce a mineral solution comprising calcium ions and/or magnesiumions, wherein the minerals comprises mafic minerals; filtering themineral solution 914 to produce a filtrate comprising sodium ions andchloride ions; concentrating the filtrate to produce the salt solution,wherein the concentrator comprises a reverse osmosis system 914;utilizing the salt solution as the anode electrolyte 104; precipitatinga carbonate and/or bicarbonate with the cathode electrolyte 912; whereinthe carbonate and/or bicarbonate comprises calcium and/or magnesiumcarbonate and/or bicarbonate. In some embodiments, the method includesdisposing of the acid in an underground storage site where the acid canbe stored in an un-reactive salt or rock formation and hence does not anenvironmental acidification.

With reference to FIGS. 1-9 and 11, the method 1100 in anotherembodiment comprises a step 1102 of producing an acid 124 in anelectrochemical system, e.g., system 900, comprising added carbondioxide 106A, 107 in the cathode electrolyte 108; and contacting amineral 906 with the acid 124. In some embodiment the method furtherproducing the acid in the anode electrolyte 104, without generating agas at the anode 102, and oxidizing hydrogen gas 112 at the anode,wherein the acid comprises hydrochloric acid 124; and wherein thehydrogen gas 112 is produced at the cathode 106; producing an alkalinesolution in the cathode electrolyte 108; migrating sodium ions into thecathode electrolyte; wherein the alkaline solution comprises sodiumhydroxide, sodium bicarbonate and/or sodium carbonate; wherein thevoltage is less than 2 V or less than 1V; wherein the anode electrolyte104 is separated from the cathode electrolyte 108 by first cationexchange membrane 116; wherein the anode 102 comprises a second cationexchange membrane 122 in contact with the anode electrolyte 102; whereinthe anode electrolyte comprises a salt, e.g., sodium chloride;dissolving a mineral 906 with the acid 124 to produce a mineralsolution; producing calcium ions and/or magnesium ions; wherein themineral comprises a mafic mineral, e.g. olivine or serpentine; filteringthe mineral solution to produce a filtrate comprising sodium ions andchloride ions solution; concentrating the filtrate to produce a saltsolution; utilizing the salt solution as the anode electrolyte 104;precipitating a carbonate and/or bicarbonate with the cathodeelectrolyte; wherein the carbonate and/or bicarbonate comprises calciumand/or magnesium carbonate and/or bicarbonate. In some embodiments, themethod includes disposing of the acid in an underground storage sitewhere the acid can be stored in an un-reactive salt or rock formationand hence does not an environmental acidification.

With reference to FIGS. 1-6, as disclosed in U.S. patent applicationSer. No. 12/503,557 filed on Jul. 16, 2009, titled: “CO2 Utilization InElectrochemical Systems”, herein incorporated by reference in itsentirety, in some embodiments, carbon dioxide is absorbed into thecathode electrolyte utilizing a gas mixer/gas absorber. In oneembodiment, the gas mixer/gas absorber comprises a series of spraynozzles that produces a flat sheet or curtain of liquid into which thegas is absorbed; in another embodiment, the gas mixer/gas absorbercomprises a spray absorber that creates a mist and into which the gas isabsorbed; in other embodiments, other commercially available gas/liquidabsorber, e.g., an absorber available from Neumann Systems, Colorado,USA is used.

The carbon dioxide used in the system may be obtained from variousindustrial sources that releases carbon dioxide including carbon dioxidefrom combustion gases of fossil fuelled power plants, e.g., conventionalcoal, oil and gas power plants, or IGCC (Integrated GasificationCombined Cycle) power plants that generate power by burning sygas;cement manufacturing plants that convert limestone to lime; oreprocessing plants; fermentation plants; and the like. In someembodiments, the carbon dioxide may comprise other gases, e.g.,nitrogen, oxides of nitrogen (nitrous oxide, nitric oxide), sulfur andsulfur gases (sulfur dioxide, hydrogen sulfide), and vaporizedmaterials. In some embodiments, the system includes a gas treatmentsystem that removes constituents in the carbon dioxide gas stream beforethe gas is utilized in the cathode electrolyte. In some embodiments, aportion of, or the entire amount of, cathode electrolyte comprisingbicarbonate ions and/or carbonate ions/and or hydroxide ions iswithdrawn from the system and is contacted with carbon dioxide gas in anexogenous carbon dioxide gas/liquid contactor to increase the absorbedcarbon dioxide content in the solution. In some embodiments, thesolution enriched with carbon dioxide is returned to the cathodecompartment; in other embodiments, the solution enriched with carbondioxide is reacted with a solution comprising divalent cations toproduce divalent cation hydroxides, carbonates and/or bicarbonates. Insome embodiments, the pH of the cathode electrolyte is adjusted upwardsby hydroxide ions that migrate from the cathode, and/or downwards bydissolving carbon dioxide gas in the cathode electrolyte to producecarbonic acid and carbonic ions that react with and remove hydroxideions. Thus it can be appreciated that the pH of the cathode electrolyteis determined, at least in part, by the balance of these two processes.

Referring to FIG. 1 herein, the system 100 in one embodiment comprises agas diffusion anode 102 and a cathode 106 in contact with a cathodeelectrolyte 108, 108A, 108B comprising dissolved carbon dioxide 107A.The system in some embodiments includes a gas delivery system 112configured to deliver hydrogen gas to the anode 102; in someembodiments, the hydrogen gas is obtained from the cathode 106. In thesystem, the anode 102 is configured to produce protons, and the cathode106 is configured to produce hydroxide ions and hydrogen gas when a lowvoltage 114, e.g., less than 2V is applied across the anode and thecathode. In the system, a gas is not produced at the anode 102.

In the system as illustrated in FIG. 1, first cation exchange membrane116 is positioned between the cathode electrolyte 108, 108 A, 108B and asalt solution 118; and an anion exchange membrane 120 is positionedbetween the salt solution 118 and the anode electrolyte 104 in aconfiguration where the anode electrolyte 104 is separated from theanode 102 by second cation exchange membrane 122. In the system, thesecond cation exchange membrane 122 is positioned between the anode 102and the anode electrolyte 104 such that anions may migrate from the saltsolution 118 to the anode electrolyte 104 through the anion exchangemembrane 120; however, anions are prevented from contacting the anode102 by the second cation exchange membrane 122 adjacent to the anode102.

In some embodiments, the system is configurable to migrate anions, e.g.,chloride ions, from the salt solution 118 to the anode electrolyte 104through the anion exchange membrane 120; migrate cations, e.g., sodiumions from the salt solution 118 to the cathode electrolyte 108, 108A,108B through the first cation exchange membrane 116; migrate protonsfrom the anode 102 to the anode electrolyte 104; and migrate hydroxideions from the cathode 106 to the cathode electrolyte 108, 108A, 108B.Thus, in some embodiments, the system can be configured to producesodium hydroxide and/or sodium bicarbonate and/or sodium carbonate inthe cathode electrolyte 108, 108A, 108B; and produce an acid e.g.,hydrochloric acid 124 in the anode electrolyte.

In some embodiments as illustrated in FIG. 1, the system comprises apartition 126 that partitions the cathode electrolyte 108 into a firstcathode electrolyte portion 108A and a second cathode electrolyteportion 108B, wherein the second cathode electrolyte portion 108B,comprising dissolved carbon dioxide, contacts the cathode 106; andwherein the first cathode electrolyte portion 108A comprising dissolvedcarbon dioxide and gaseous carbon dioxide is in contact with the secondcathode electrolyte portion 108B under the partition 126. In the system,the partition is positioned in the cathode electrolyte such that a gas,e.g., carbon dioxide in the first cathode electrolyte portion 108A isisolated from cathode electrolyte in the second cathode electrolyteportion 108B. Thus, for example, where a gas, e.g., hydrogen, isgenerated at the cathode and it is desired to separate this cathode gasfrom a gas or vapor that may evolve from the cathode electrolyte, thepartition may serve as a means to prevent mixing of the gases form thecathode and the gases and or vapor from the cathode electrolyte. Whilethis system is illustrated in FIG. 1, it is applicable to any of theelectrochemical system described herein, e.g., the systems illustratedin FIGS. 4, 7 and 8.

Thus, as can be appreciated, in some embodiments, on applying thepresent voltage across the anode and cathode, the system can beconfigured to produce hydroxide ions and hydrogen gas at the cathode106; migrate hydroxide ions from the cathode into the cathodeelectrolyte 108, 108B, 108A; migrate cations from the salt solution 118to the cathode electrolyte through the first cation exchange membrane116; migrate chloride ions from the salt solution 118 to the anodeelectrolyte 104 through the anion exchange membrane 120; and migrateprotons from the anode 102 to the anode electrolyte 104. Hence,depending on the salt solution 118 used, the system can be configured toproduce an alkaline solution, e.g., sodium hydroxide in the cathodeelectrolyte.

In some embodiments, the system is operatively connected to a carbondioxide gas/liquid contactor 128 configured to remove cathodeelectrolyte from the system and dissolve carbon dioxide in the cathodeelectrolyte in the gas/liquid contactor before the cathode electrolyteis returned to the system.

In other embodiments, the cathode electrolyte is operatively connectedto a system (not shown) that is configured to precipitate divalentcation carbonates and/or divalent cation bicarbonates and/or divalentcation hydroxides from a solution comprising carbon dioxide gas anddivalent cations.

FIG. 2 illustrates a schematic of a suitable gas diffusion anode thatcan be used in embodiments of the system described herein. In someembodiments, the gas diffusion anode comprises a conductive substrate130 infused with a catalyst 136 that is capable of catalyzing theoxidation of hydrogen gas to protons when the present voltages areapplied across the anode and cathode. In some embodiments, the anodecomprises a first side 132 that interfaces with hydrogen gas provided tothe anode, and an opposed second side 134 that interfaces with the anodeelectrolyte 104. In some embodiments, the portion of the substrate 132that interfaces with the hydrogen gas is hydrophobic and is relativelydry; and the portion of the substrate 134 that interfaces with the anodeelectrolyte 104 is hydrophilic and may be wet, which facilitatesmigration of protons from the anode to the anode electrolyte. In variousembodiments, the substrate is porous to facilitate the movement of gasfrom the first side 132 to the catalyst 136 that may be located onsecond side 134 of the anode; in some embodiments, the catalyst may alsobe located within the body of the substrate 130. The substrate 130 maybe selected for its hydrophilic or hydrophobic characteristics asdescribed herein, and also for its low ohmic resistance to facilitateelectron conduction from the anode through a current collector connectedto the voltage supply 114; the substrate may also be selected for itporosity to ion migration, e.g., proton migration, from the anode to theanode electrolyte 116.

In some embodiments, the catalyst may comprise platinum, ruthenium,iridium, rhodium, manganese, silver or alloys thereof. Suitable gasdiffusion anodes are available commercially, e.g., from E-TEK (USA) andother suppliers. In some embodiments of the anode as is illustrated inFIG. 8, the anode comprises a ion exchange membrane, e.g., a cationexchange membrane 122 that contacts the second side 134 of the anode. Insuch embodiments, the ion exchange membrane can be used to allow orprevent migration of ions to or from the anode. Thus, for example, withreference to FIG. 8, when protons are generated at the anode, a cationexchange membrane may be used to facilitate the migration of the protonsfrom the anode and/or block the migration of ions, e.g., cations to thesubstrate. In the some embodiments, the ion exchange membrane may beselected to preferentially allow passage of one type of cation, e.g.,hydrogen ions, while preventing the passage of another type of ions,e.g., sodium ions.

As is illustrated in FIG. 1, the system includes a salt solution 118located between the anode electrolyte 104 and the cathode electrolyte108, 108A, 108B. In some embodiments, the cathode electrolyte isseparated from the salt solution by a first cation exchange membrane 116that is allows migration of cations, e.g., sodium ions, from the saltsolution to the cathode electrolyte. The first cation exchange membrane116 is also capable of blocking the migration of anions from the cathodeelectrolyte 108, 108A, 108B to the salt solution 118. In someembodiments, the anode electrolyte 104 is separated from the saltsolution 118 by an anion exchange membrane 108 that will allow migrationof anions, e.g., chloride ions, from the salt solution 118 to the anodeelectrolyte 104. The anion exchange membrane, however, will block themigration of cations, e.g., protons from the anode electrolyte 104 tothe salt solution 118.

With reference to FIGS. 1 and 2, the system includes a hydrogen gassupply system 112 configured to provide hydrogen gas to the anode 102.The hydrogen may be obtained from the cathode 106 or may be obtainedfrom external source, e.g., from a commercial hydrogen gas supplier,e.g., at start-up of the system when the hydrogen supply from thecathode is insufficient. In the system, the hydrogen gas is oxidized toprotons and electrons; un-reacted hydrogen gas is recovered andcirculated 140 at the anode.

Referring to FIG. 1, in operation, the cathode electrolyte 108, 108A,108B is initially charged with a alkaline electrolyte, e.g., sodiumhydroxide solution, and the anode electrolyte 104 is initially chargedwith an acidic electrolyte, e.g., dilute hydrochloric acid. The cathodeelectrolyte is also initially charged with carbon dioxide gas 107A, 128,and hydrogen gas is provided to the anode. In the system, on applying avoltage across the anode and cathode, protons produced at the anode willenter into the anode electrolyte and attempt to migrate from the anodeelectrolyte 104 to the cathode 106 via the salt solution 118 between thecathode and anode. However, since the anion exchange membrane will blockthe migration of protons to the salt solution, the protons willaccumulate in the anode electrolyte 104.

Simultaneously at the cathode 106, the voltage across the anode andcathode will produce hydroxide ions and hydrogen gas at the cathode. Insome embodiments, the hydrogen produced at the cathode is recovered anddirected to the anode 102 where it is oxidized to protons. In thesystem, hydroxide ions produced at the cathode 106 will enter into thecathode electrolyte 108, 108A, 108B from where they will attempt tomigrate to the anode 102 via the salt solution 118 between the cathodeand anode. However, since the cathode electrolyte 108, 108A, 108B isseparated from the salt solution electrolyte by the first cationexchange membrane 116 which will block the passage of anions, the firstcation exchange membrane will block the migration of hydroxide ions fromthe cathode electrolyte to the salt solution; consequently, thehydroxide ions will accumulate in the cathode electrolyte 108, 108A,108B.

In the system as illustrated in FIG. 1, with the voltage across theanode and cathode, since the salt solution is separated from the cathodeelectrolyte by the first cation exchange membrane 116, cations in thesalt solution, e.g., sodium ions, will migrate through the first cationexchange membrane 116 to the cathode electrolyte 108, 108A, 108B, andanions, e.g., chloride ions, will migrate to the anode electrolytethrough the anion exchange membrane 120. Consequently, in the system, asillustrated in FIG. 1, an acid, e.g., hydrochloric acid 124 will beproduced in the anode electrolyte 104, and alkaline solution, e.g.,sodium hydroxide will be produced in the cathode electrolyte. As can beappreciated, with the migration of cations and anions from the saltsolution, the system in some embodiments can be configured to produce apartly de-ionized salt solution from the salt solution 118. In someembodiments, this partially de-ionized salt solution can be used asfeed-water to a desalination facility (not shown) where it can befurther processed to produce desalinated water as described in commonlyassigned U.S. patent application Ser. No. 12/163,205 filed on Jun. 27,2008, herein incorporated by reference in its entirety; alternatively,the solution can be used in industrial and agricultural applicationswhere its salinity is acceptable.

With reference to FIG. 1, the system in some embodiments includes asecond cation exchange membrane 124, attached to the anode substrate105, such that it separates the anode 102 from the anode electrolyte. Inthis configuration, as the second cation exchange membrane 122 ispermeable to cations, protons formed at the anode will migrate to theanode electrolyte as described herein; however, as the second cationexchange membrane 122 is impermeable to anions, anions, e.g., chlorideions, in the anode electrolyte will be blocked from migrating to theanode 102, thereby avoiding interaction between the anode and the anionsthat may interact with the anode, e.g., by corrosion.

With reference to FIG. 1, in some embodiments, the system includes apartition 128 configured into J-shape structure and positioned in thecathode electrolyte 108, 108A, 108B to define an upward-tapering channel144 in the upper portion of the cathode electrolyte compartment. Thepartition also defines a downward-tapering channel 146 in lower portionof the cathode electrolyte. Thus, with the partition in the place, thecathode electrolyte 108 is partitioned into the first cathodeelectrolyte portion 108A and a second cathode electrolyte portion 108B.As is illustrated in FIG. 1, cathode electrolyte in the first cathodeelectrolyte portion 108A is in contact with cathode electrolyte in thesecond cathode electrolyte portion 108B; however, a gas in the firstelectrolyte portion 108A, e.g., carbon dioxide, is prevented from mixingwith cathode electrolyte in the second cathode electrolyte 108B.Although this is illustrated in for the system of FIG. 1, such aconfiguration may be used in any system where it is desired to partitionan electrolyte solution, e.g., a cathode electrolyte such that a gasthat is introduced into one portion remains separate from anotherportion. For example, such a configuration may be used in any system asdescribed herein as, e.g., in FIGS. 7 and 8.

With reference to FIG. 1, the system in some embodiments includes acathode electrolyte circulating system 142 adapted for withdrawing andcirculating cathode electrolyte in the system. In one embodiment, thecathode electrolyte circulating system comprises a carbon dioxidegas/liquid contactor 128 that is adapted for dissolving carbon dioxidein the circulating cathode electrolyte, and for circulating theelectrolyte in the system. As can be appreciated, since the pH of thecathode electrolyte can be adjusted by withdrawing and/or circulatingcathode electrolyte from the system, the pH of the cathode electrolytecompartment can be by regulated by regulating an amount of cathodeelectrolyte removed from the system through the carbon dioxidegas/liquid contactor 128.

In an alternative as illustrated in FIG. 4, the system comprises acathode 106 in contact with a cathode electrolyte 108 and an anode 102in contact with an anode electrolyte 104. In this system, the cathodeelectrolyte comprises a salt solution that functions as the cathodeelectrolyte as well as a source of chloride and sodium ions for thealkaline and acid solution produced in the system. In this system, thecathode electrolyte is separated from the anode electrolyte by an anionexchange membrane 120 that allows migration of anions, e.g., chlorideions, from the salt solution to the anode electrolyte. As is illustratedin FIG. 4, the system includes a hydrogen gas delivery system 112configured to provide hydrogen gas to the anode. The hydrogen may beobtained from the cathode and/or obtained from an external source, e.g.,a commercial hydrogen gas supplier e.g., at start-up of operations whenthe hydrogen supply from the cathode is insufficient. In someembodiments, the hydrogen delivery system is configured to deliver gasto the anode where oxidation of the gas is catalyzed to protons andelectrons. In some embodiments, un-reacted hydrogen gas in the system isrecovered and re-circulated to the anode.

Referring to FIG. 4, as with the system of FIG. 1, on applying a voltageacross the anode and cathode, protons produced at the anode fromoxidation of hydrogen will enter into the anode electrolyte from wherethey will attempt to migrate to the cathode electrolyte across the anionexchange membrane 120. However, since the anion exchange membrane 120will block the passage of cations, the protons will accumulate in theanode electrolyte. At the same time, however, the anion exchangemembrane 120 being pervious to anions will allow the migration ofanions, e.g., chloride ions from the cathode electrolyte to the anode,thus in this embodiment, chloride ions will migrate to the anodeelectrolyte to produce hydrochloric acid in the anode electrolyte. Inthis system, the voltage across the anode and cathode is adjusted to alevel such that hydroxide ions and hydrogen gas are produced at thecathode without producing a gas, e.g., chlorine or oxygen, at the anode.In this system, since cations will not migrate from the cathodeelectrolyte across the anion exchange membrane 116, sodium ions willaccumulate in the cathode electrolyte 108 to produce an alkalinesolution with hydroxide ions produced at the cathode. In embodimentswhere carbon dioxide gas is dissolved in the cathode electrolyte, sodiumions may also produce sodium bicarbonate and or sodium carbonate in thecathode electrolyte as described herein with reference to FIG. 1.

With reference to FIG. 1, depending on the pH of the cathodeelectrolyte, carbon dioxide gas introduced into the first cathodeelectrolyte portion 108A will dissolve in the cathode electrolyte andreversibly dissociate and equilibrate to produce carbonic acid, protons,carbonate and/or bicarbonate ions in the first cathode electrolytecompartment as follows:CO₂+H₂O

H₂CO₃

H⁺+HCO₃ ⁻

H⁺+CO₃ ²⁻In the system, as cathode electrolyte in the first cathode electrolyteportion 108A may mix with second cathode electrolyte portion 108B, thecarbonic acid, bicarbonate and carbonate ions formed in the firstcathode electrolyte portion 108A by absorption of carbon dioxide in thecathode electrolyte may migrate and equilibrate with cathode electrolytein the second cathode electrolyte portion 108B. Thus, in someembodiments, first cathode electrolyte portion 108A may comprisedissolved and un-dissolved carbon dioxide gas, and/or carbonic acid,and/or bicarbonate ions and/or carbonate ions; while second cathodeelectrolyte portion 108B may comprise dissolved carbon dioxide, and/orcarbonic acid, and/or bicarbonate ions and/or carbonate ions.

With reference to FIG. 1, on applying a voltage across anode 102 andcathode 108, the system 100 may produce hydroxide ions and hydrogen gasat the cathode from water, as follows:2H₂O+2e ⁻=H₂+2OH⁻As cathode electrolyte in first cathode electrolyte portion 108A canintermix with cathode electrolyte in second cathode electrolyte portion108B, hydroxide ions formed in the second cathode electrolyte portionmay migrate and equilibrate with carbonate and bicarbonate ions in thefirst cathode electrolyte portion 108A. Thus, in some embodiments, thecathode electrolyte in the system may comprise hydroxide ions anddissolved and/or un-dissolved carbon dioxide gas, and/or carbonic acid,and/or bicarbonate ions and/or carbonate ions. In the system, as thesolubility of carbon dioxide and the concentration of bicarbonate andcarbonate ions in the cathode electrolyte are dependent on the pH of theelectrolyte, the overall reaction in the cathode electrolyte 104 iseither:Scenario 1: 2H₂O+2CO₂+2e ⁻=H₂+2HCO₃ ⁻; orScenario 2: H₂O+CO₂+2e ⁻=H₂+CO₃ ²⁻or a combination of both, depending on the pH of the cathodeelectrolyte. This is illustrated in as a carbonate speciation diagram inFIG. 5.

For either scenario, the overall cell potential of the system can bedetermined through the Gibbs energy change of the reaction by theformula:E _(cell) =−ΔG/nFOr, at standard temperature and pressure conditions:E ^(o) _(cell) =−ΔG ^(o) /nFwhere, E_(cell) is the cell voltage, ΔG is the Gibbs energy of reaction,n is the number of electrons transferred, and F is the Faraday constant(96485 J/Vmol). The E_(cell) of each of these reactions is pH dependentbased on the Nernst equation as illustrated in FIG. 6.

Also, for either scenario, the overall cell potential can be determinedthrough the combination of Nernst equations for each half cell reaction:E=E ^(o) −RT ln(Q)/nFwhere, E^(o) is the standard reduction potential, R is the universal gasconstant, (8.314 J/mol K) T is the absolute temperature, n is the numberof electrons involved in the half cell reaction, F is Faraday's constant(96485 J/Vmol), and Q is the reaction quotient such that:E _(total) =E _(cathode) +E _(anode.)When hydrogen is oxidized to protons at the anode as follows:H₂=2H⁺+2e ⁻,E^(o) is 0.00 V, n is 2, and Q is the square of the activity of H⁺ sothat:E _(anode)=+0.059 pH_(a),where pH_(a) is the pH of the anode electrolyte.When water is reduced to hydroxide ions and hydrogen gas at the cathodeas follows:2H₂O+2e ⁻=H₂+2OH⁻,E^(o) is −0.83 V, n is 2, and Q is the square of the activity of OH⁻ sothat:E _(cathode)=−0.059 pH_(c),where pH_(c) is the pH of the cathode electrolyte.

For either Scenario, the E for the cathode and anode reactions varieswith the pH of the anode and cathode electrolytes. Thus, for Scenario 1if the anode reaction, which is occurring in an acidic environment, isat a pH of 0, then the E of the reaction is 0V for the half cellreaction. For the cathode reaction, if the generation of bicarbonateions occur at a pH of 7, then the theoretical E is 7×(−0.059 V)=−0.413Vfor the half cell reaction where a negative E means energy is needed tobe input into the half cell or full cell for the reaction to proceed.Thus, if the anode pH is 0 and the cathode pH is 7 then the overall cellpotential would be −0.413V, where:E _(total)=−0.059(pH_(a)−pH_(c))=−0.059 ΔpH.

For Scenario 2 in which carbonate ions are produced, if the anode pH is0 and the cathode pH is 10, this would represent an E of 0.59 V.

Thus, in some embodiments, directing CO₂ gas into the cathodeelectrolyte may lower the pH of the cathode electrolyte by producingbicarbonate ions and/or carbonate ions in the cathode electrolyte, whichconsequently may lower the voltage across the anode and cathode inproducing hydroxide, carbonate and/or bicarbonate in the cathodeelectrolyte.

Thus, as can be appreciated, if the cathode electrolyte is allowed toincrease to a pH of 14 or greater, the difference between the anodehalf-cell potential (represented as the thin dashed horizontal line,Scenario 1, above) and the cathode half cell potential (represented asthe thick solid sloping line in Scenario 1, above) will increase to0.83V. With increased duration of cell operation without CO₂ addition orother intervention, e.g., diluting with water, the required cellpotential will continue to increase. The cell potential may alsoincrease due to ohmic resistance loses across the membranes in theelectrolyte and the cell's overvoltage potential.

Herein, an overvoltage potential refers to the voltage differencebetween a thermodynamically determined half-cell reduction potential,and the experimentally observed potential at which the redox reactionoccurs. The term is related to a cell voltage efficiency as theovervoltage potential requires more energy than is thermodynamicallyrequired to drive a reaction. In each case, the extra energy is lost asheat. Overvoltage potential is specific to each cell design and willvary between cells and operational conditions even for the samereaction.

In embodiments wherein it is desired to produce bicarbonate and/orcarbonate ions in the cathode electrolyte, the system as illustrated inFIGS. 1-2, and as described above with reference to production ofhydroxide ions in the cathode electrolyte, can be configured to producebicarbonate ions and/or carbonate ions in the first cathode electrolyteby dissolving carbon dioxide in the first cathode electrolyte andapplying a voltage of less than 3V, or less than 2.5 V, or less than 2V,or less than 1.5V such as less than 1.0V, or even less than 0.8 V or0.6V across the cathode and anode.

In some embodiments, hydroxide ions, carbonate ions and/or bicarbonateions produced in the cathode electrolyte, and hydrochloric acid producedin the anode electrolyte are removed from the system, while sodiumchloride in the salt solution electrolyte is replenished to maintaincontinuous operation of the system. As can be appreciated, in someembodiments, the system can be configured to operate in variousproduction modes including batch mode, semi-batch mode, continuous flowmode, with or without the option to withdraw portions of the hydroxidesolution produced in the cathode electrolyte, or withdraw all or aportions of the acid produced in the anode electrolyte, or direct thehydrogen gas produced at the cathode to the anode where it may beoxidized.

In some embodiments, hydroxide ions, bicarbonate ions and/or carbonateion solutions are produced in the cathode electrolyte when the voltageapplied across the anode and cathode is less than 3V, 2.9V or less, 2.8Vor less, 2.7V or less, 2.6V or less, 2.5V or less, 2.4V or less, 2.3V orless, 2.2V or less, 2.1V or less, 2.0V or less, 1.9V or less, 1.8V orless, 1.7V or less, 1.6V, or less 1.5V or less, 1.4V or less, 1.3V orless, 1.2V or less, 1.1V or less, 1.0V or less, 0.9V or less or less,0.8V or less, 0.7V or less, 0.6V or less, 0.5V or less, 0.4V or less,0.3V or less, 0.2V or less, or 0.1 V or less.

In another embodiment, the voltage across the anode and cathode can beadjusted such that gas will form at the anode, e.g., oxygen or chlorine,while hydroxide ions, carbonate ions and bicarbonate ions are producedin the cathode electrolyte and hydrogen gas is generated at the cathode.However, in this embodiment, hydrogen gas is not supplied to the anode.As can be appreciated by one ordinarily skilled in the art, in thisembodiment, the voltage across the anode and cathode will be generallyhigher compared to the embodiment when a gas does not form at the anode.

With reference to FIGS. 1-2, in some embodiments, the invention providesfor a system comprising one or more anion exchange membrane 120, andcation exchange membranes 116, 122 located between the gas diffusionanode 102 and the cathode 106. In some embodiments, the membranes shouldbe selected such that they can function in an acidic and/or basicelectrolytic solution as appropriate. Other desirable characteristics ofthe membranes include high ion selectivity, low ionic resistance, highburst strength, and high stability in an acidic electrolytic solution ina temperature range of 0° C. to 100° C. or higher, or a alkalinesolution in similar temperature range may be used. In some embodiments,a membrane that is stable in the range of 0° C. to 80° C., or 0° C. to90° C., but not stable above these ranges may be used. For otherembodiments, it may be useful to utilize an ion-specific ion exchangemembranes that allows migration of one type of cation but not another;or migration of one type of anion and not another, to achieve a desiredproduct or products in an electrolyte. In some embodiments, the membraneshould be stable and functional for a desirable length of time in thesystem, e.g., several days, weeks or months or years at temperatures inthe range of 0° C. to 80° C., or 0° C. to 90° C. and higher and/orlower. In some embodiments, for example, the membranes should be stableand functional for at least 5 days, 10 days, 15 days, 20 days, 100 days,1000 days or more in electrolyte temperatures at 80° C., 70° C., 60° C.,50° C., 40° C., 30° C., 20° C., 10° C., 5° C. and more or less.

As can be appreciated, the ohmic resistance of the membranes will affectthe voltage drop across the anode and cathode, e.g., as the ohmicresistance of the membranes increase, the voltage drop across the anodeand cathode will increase, and vice versa. Membranes currently availablecan be used and they include membranes with relatively low ohmicresistance and relatively high ionic mobility; similarly, membranescurrently available with relatively high hydration characteristics thatincrease with temperatures, and thus decreasing the ohmic resistance canbe used. Consequently, as can be appreciated, by selecting currentlyavailable membranes with lower ohmic resistance, the voltage drop acrossthe anode and cathode at a specified temperature can be lowered.

Scattered through currently available membrane are ionic channelsconsisting of acid groups. These ionic channels may extend from theinternal surface of the matrix to the external surface and the acidgroups may readily bind water in a reversible reaction aswater-of-hydration. This binding of water as water-of-hydration followsfirst order reaction kinetics, such that the rate of reaction isproportional to temperature. Consequently, currently available membranescan be selected to provide a relatively low ohmic and ionic resistancewhile providing for improved strength and resistance in the system for arange of operating temperatures. Suitable membranes are commerciallyavailable from Asahi Kasei of Tokyo, Japan; or from MembraneInternational of Glen Rock, N.J., and USA.

In some embodiments, the cathode electrolyte 108, 108A, 108B isoperatively connected to a waste gas treatment system (not illustrated)where the alkaline solution produced in the cathode electrolyte isutilized, e.g., to sequester carbon dioxide contained in the waste gasby contacting the waste gas and the cathode electrolyte with a solutionof divalent cations to precipitate hydroxides, carbonates and/orbicarbonates as described in commonly assigned U.S. patent applicationSer. No. 12/344,019 filed on Dec. 24, 2008, herein incorporated byreference in its entirety. The precipitates, comprising, e.g., calciumand magnesium hydroxides, carbonates and bicarbonates in someembodiments may be utilized as building materials, e.g., as cements andaggregates, as described in commonly assigned U.S. patent applicationSer. No. 12/126,776 filed on May 23, 2008, supra, herein incorporated byreference in its entirety. In some embodiments, some or all of thecarbonates and/or bicarbonates are allowed to remain in an aqueousmedium, e.g., a slurry or a suspension, and are disposed of in anaqueous medium, e.g., in the ocean depths or a subterranean site.

In some embodiments, the cathode and anode are also operativelyconnected to an off-peak electrical power-supply system 114 thatsupplies off-peak voltage to the electrodes. Since the cost of off-peakpower is lower than the cost of power supplied during peak power-supplytimes, the system can utilize off-peak power to produce an alkalinesolution in the cathode electrolyte at a relatively lower cost.

In another embodiment, the system produces an acid, e.g., hydrochloricacid 124 in the anode electrolyte 104. In some embodiments, the anodecompartment is operably connected to a system for dissolving mineralsand/or waste materials comprising divalent cations to produce a solutionof divalent cations, e.g., Ca++ and Mg++. In some embodiments, thedivalent cation solution is utilized to precipitate hydroxides,carbonates and/or bicarbonates by contacting the divalent cationsolution with the present alkaline solution and a source of carbondioxide gas as described in U.S. patent application Ser. No. 12/344,019filed on Dec. 24, 2008, supra, herein incorporated by reference in itsentirety. In some embodiments, the precipitates are used as buildingmaterials e.g., cement and aggregates as described in commonly assignedU.S. patent application Ser. No. 12/126,776, supra, herein incorporatedby reference in its entirety.

With reference to FIG. 1, on applying a voltage across the anode 102 andcathode 106, protons will form at the anode from oxidation of hydrogengas supplied to the anode, while hydroxide ions and hydrogen gas willform at the cathode electrolyte from the reduction of water, as follows:H₂=2H⁺+2e ⁻ (anode, oxidation reaction)2H₂O+2e ⁻=H₂+2OH⁻ (cathode, reduction reaction)

Since protons are formed at the anode from hydrogen gas provided to theanode; and since a gas such as oxygen does not form at the anode; andsince water in the cathode electrolyte forms hydroxide ions and hydrogengas at the cathode, the system will produce hydroxide ions in thecathode electrolyte and protons in the anode electrolyte when a voltageis applied across the anode and cathode. Further, as can be appreciated,in the present system since a gas does not form at the anode, the systemwill produce hydroxide ions in the cathode electrolyte and hydrogen gasat the cathode and hydrogen ions at the anode when less than 2V isapplied across the anode and cathode, in contrast to the higher voltagethat is required when a gas is generated at the anode, e.g., chlorine oroxygen. For example, in some embodiments, hydroxide ions are producedwhen less than 2.0V, 1.5V, 1.4V, 1.3V, 1.2V, 1.1V, 1.0V, 0.9V, 0.8V,0.7V, 0.6V, 0.5V, 0.4V, 0.3V, 0.2V, 0.1 V or less is applied across theanode and cathode.

As discussed above, in the system, on applying a voltage across theanode 102 and cathode 106, the positively charged protons formed at theanode will attempt to migrate to the cathode through the anodeelectrolyte 104, while the negatively charged hydroxide ions formed atthe cathode will attempt to migrate to the anode through the cathodeelectrolyte 108, 108A, 108B. As is illustrated in FIG. 1 and withreference to hydroxide ions in the cathode electrolyte 108, 108A, 108B,since the first cation exchange membrane 116 will restrict the migrationof anions from the cathode electrolyte 108, 108A, 108B, and since theanion exchange membrane 120 will prevent the migration of anions fromthe anode electrolyte 104 to the salt solution 118, the hydroxide ionsgenerated in the cathode electrolyte will be prevented from migratingout of the cathode electrolyte through the cation exchange membrane.Consequently, on applying the voltage across the anode and cathode, thehydroxide ions produced at the cathode will be contained in the cathodeelectrolyte. Thus, depending on the flow rate of fluids into and out ofthe cathode electrolyte and the rate of carbon dioxide dissolution inthe cathode electrolyte, the pH of the cathode electrolyte will adjust,e.g., the pH may increase, decrease or remain the same.

In some embodiments, depending on the ionic species desired in cathodeelectrolyte 108, 108A, 108B and/or the anode electrolyte 104 and/or thesalt solution 118, alternative reactants can be utilized. Thus, forexample, if a potassium salt such as potassium hydroxide or potassiumcarbonate is desired in the cathode electrolyte 1108, 108A, 108B, then apotassium salt such as potassium chloride can be utilized in the saltsolution 118. Similarly, if sulfuric acid is desired in the anodeelectrolyte, then a sulfate such as sodium sulfate can be utilized inthe salt solution 118. As described in some embodiments herein, carbondioxide gas is absorbed in the cathode electrolyte; however, it will beappreciated that other gases, including volatile vapors, can be absorbedin the electrolyte, e.g., sulfur dioxide, or organic vapors to produce adesired result. As can be appreciated, the gas can be added to theelectrolyte in various ways, e.g., by bubbling it directly into theelectrolyte, or dissolving the gas in a separate compartment connectedto the cathode compartment and then directed to the cathode electrolyteas described herein.

With reference to FIGS. 1 and 3, method 300 in some embodimentscomprises a step 302 of applying a voltage across a cathode 106 and agas diffusion anode 102 in an electrochemical system 100, wherein thecathode contacts a cathode electrolyte comprising dissolved carbondioxide. In some embodiments, the method includes a step of providinghydrogen to the gas diffusion anode 102; a step of contacting thecathode 106 with a cathode electrolyte 108, 108A, 108B comprisingdissolved carbon dioxide gas 107A; and a step of applying a voltage 114across the anode and cathode; a step whereby protons are produced at theanode and hydroxide ions and hydrogen gas produced at the cathode; astep whereby a gas is not produced at the anode when the voltage isapplied across the anode and cathode; a step wherein the voltage appliedacross the anode and cathode is less than 2V; a step comprisingdirecting hydrogen gas from the cathode to the anode; a step comprisingwhereby protons are migrated from the anode to an anode electrolyte; astep comprising interposing an anion exchange membrane between the anodeelectrolyte and the salt solution; a step comprising interposing a firstcation exchange membrane between the cathode electrolyte and the saltsolution, wherein the salt solution is contained between the anionexchange membrane and the first cation exchange membrane; a stepcomprising whereby anions migrate from the salt solution to the anodeelectrolyte through the anion exchange membrane, and cations migratefrom the salt solution to the cathode electrolyte through the firstcation exchange membrane; a step comprising producing hydroxide ionsand/or carbonate ions and/or bicarbonate ions in the cathodeelectrolyte; a step comprising producing an acid in the anodeelectrolyte; a step comprising producing sodium hydroxide and/or sodiumcarbonate and/or sodium bicarbonate in the cathode electrolyte; a stepwhereby hydrochloric acid is produced in the anode electrolyte; a stepcomprising contacting the cathode electrolyte with a divalent cationsolution, wherein the divalent cations comprise calcium and magnesiumions; a step comprising producing partially desalinated water from thesalt solution; a step comprising withdrawing a first portion of thecathode electrolyte and contacting the first portion of cathodeelectrolyte with carbon dioxide; and a step comprising contacting thefirst portion of cathode electrolyte with a divalent cation solution.

In some embodiments, hydroxide ions are formed at the cathode 106 and inthe cathode electrolyte 108, 108A, 108B by applying a voltage of lessthan 2V across the anode and cathode without forming a gas at the anode,while providing hydrogen gas at the anode for oxidation at the anode. Insome embodiments, method 300 does not form a gas at the anode when thevoltage applied across the anode and cathode is less than 3V or less,2.9V or less, 2.8V or less, 2.7V or less, 2.6V or less, 2.5V or less,2.4V or less, 2.3V or less, 2.2V or less, 2.1V or less, 2.0V or less,1.9V or less, 1.8V or less, 1.7V or less, 1.6V or less, 1.5V or less,1.4V or less, 1.3V or less, 1.2V or less, 1.1V or less, 1.0V or less,0.9V or less, 0.8V or less, 0.7V or less, 0.6V or less, 0.5V or less,0.4V or less, 0.3V or less, 0.2V or less, or 0.1 V or less, whilehydrogen gas is provided to the anode where it is oxidized to protons.As will be appreciated by one ordinarily skilled in the art, by notforming a gas at the anode and by providing hydrogen gas to the anodefor oxidation at the anode, and by otherwise controlling the resistancein the system for example by decreasing the electrolyte path lengths andby selecting ionic membranes with low resistance and any other methodknow in the art, hydroxide ions can be produced in the cathodeelectrolyte with the present lower voltages.

In some embodiments, hydroxide ions, bicarbonate ions and carbonate ionsare produced in the cathode electrolyte where the voltage applied acrossthe anode and cathode is less than 3.0V, 2.9V, 2.8V, 2.7V, 2.6V, 2.5V,2.4V, 2.3V, 2.2V, 2.1V, 2.0V, 1.9V, 1.8V, 1.7V, 1.6V, 1.5V, 1.4V, 1.3V,1.2V, 1.1V, 1.0V, 0.9V, 0.8V, 0.7V, 0.6V, 0.5V, 0.4V, 0.3V, 0.2V, 0.1Vor less without forming a gas at the anode. In some embodiments, themethod is adapted to withdraw and replenish at least a portion of thecathode electrolyte and the acid in the anode electrolyte back into thesystem in either a batch, semi-batch or continuous mode of operation.

In an exemplarary embodiment, a system configured substantially asillustrated in FIGS. 1 and 2 was operated with a constant currentdensity applied across the electrodes at steady state conditions whilecarbon dioxide gas was continuously dissolved into the cathodeelectrolyte, at various temperatures and voltages. In the system, aplatinum catalyst, gas diffusion anode obtained from E-TEK Corporation,(USA) was used as the anode. A Raney nickel deposited onto a nickelgauze substrate was used as the cathode. In the system, the initial acidconcentration in the anode electrolyte was 1 M; the initial sodiumchloride salt solution was 5 M; and the initial concentration of thesodium hydroxide solution in the cathode compartment was 1 M. In thesystem, the pH of the cathode compartment was maintained at either 8 or10 by regulating the amount of carbon dioxide dissolved in the cathodeelectrolyte.

TABLE 1 Experimental Current Density, Temperature and VoltageCharacteristics of the System Current density T (° C.) Potential (V) pH(mA/cm²) 25 0.8 10 8.6 8 11.2 1.2 10 28.3 8 29.2 1.6 10 50.2 8 50.6 750.8 10 13.3 8 17.8 1.2 10 45.3 8 49.8 1.6 10 80.8 8 84.7

As is illustrated in Table 1, a range of current densities was achievedacross the electrode in the system. As will be appreciated by oneordinarily skilled in the art, the current density that can be achievedwith other configurations of the system may vary, depending on severalfactors including the cumulative electrical resistance losses in thecell, environmental test conditions, the over-potential associated withthe anodic and cathodic reactions, and other factors.

It will also be appreciated that the current densities achieved in thepresent configuration and as set forth in Table 1 are correlated withthe production of hydroxide ions at the cathode, and thus are correlatedwith the production of sodium hydroxide and/or sodium carbonate and/orsodium bicarbonate in the cathode electrolyte, as follows. Withreference to Table 1, at 75° C., 0.8 V and a pH of 10, each cm² ofelectrode passed 13.3 mA of current, where current is a measure ofcharge passed (Coulomb) per time (second). Based on Faraday's Laws, theamount of product, e.g., hydroxide ions, produced at an electrode isproportional to the total electrical charge passed through the electrodeas follows:

n=(I*t)/(F*z)

where n is moles of product, I is a current, t is time, F is Faraday'sconstant, and z is the electrons transferred per product ionic species(or reagent ionic species). Thus, based on the present example,1.38×10⁻⁴ moles of hydroxide ions are produced per second per cm² ofelectrode, which is correlated with the production of sodium hydroxidein the cathode electrolyte. In the system the production rate of NaOHdictates the production rate of NaHCO₃ and Na₂CO₃ through Le Chatelier'sprinciple following the net chemical equilibria equations ofH₂CO₃+OH⁻═H₂O+HCO₃ ⁻and HCO₃ ⁻+OH⁻═H₂O+CO₃ ²⁻,where an increase in concentration of one species in equilibria willchange the concentration of all species so that the equilibrium productmaintains the equilibrium constant. Thus, in the system, the equilibriumconcentrations of H₂CO₃, HCO₃ ⁻, and CO₃ ²⁻ vs. pH in the electrolytewill follow the carbonate speciation diagram as discussed above.

In the system as illustrated in FIG. 1 and as discussed with referenceto the carbonate speciation graph, supra, the solubility of carbondioxide in the cathode electrolyte is dependent on the pH of theelectrolyte. Also in the system, the voltage across the cathode andanode is dependent on several factors including the pH differencebetween the anode electrolyte and cathode electrolyte. Thus, in someembodiments the system can be configured to operate at a specified pHand voltage to absorb carbon dioxide and produce carbonic acid,carbonate ions and/or bicarbonate ions in the cathode electrolyte. Inembodiments where carbon dioxide gas is dissolved in the cathodeelectrolyte, as protons are removed from the cathode electrolyte morecarbon dioxide may be dissolved to form carbonic acid, bicarbonate ionsand/or carbonate ions. Depending on the pH of the cathode electrolytethe balance is shifted toward bicarbonate ions or toward carbonate ions,as is well understood in the art and as is illustrated in the carbonatespeciation diagram, above. In these embodiments the pH of the cathodeelectrolyte solution may decrease, remain the same, or increase,depending on the rate of removal of protons compared to rate ofintroduction of carbon dioxide. It will be appreciated that no carbonicacid, hydroxide ions, carbonate ions or bicarbonate ions are formed inthese embodiments, or that carbonic acid, hydroxide ions, carbonateions, bicarbonate ions may not form during one period but form duringanother period.

In another embodiment, the present system and method are integrated witha carbonate and/or bicarbonate precipitation system (not illustrated)wherein a solution of divalent cations, when added to the presentcathode electrolyte, causes formation of precipitates of divalentcarbonate and/or bicarbonate compounds, e.g., calcium carbonate ormagnesium carbonate and/or their bicarbonates. In some embodiments, theprecipitated divalent carbonate and/or bicarbonate compounds may beutilized as building materials, e.g., cements and aggregates asdescribed for example in commonly assigned U.S. patent application Ser.No. 12/126,776 filed on May 23, 2008, herein incorporated by referencein its entirety.

In an alternative embodiment, the present system and method areintegrated with a mineral and/or material dissolution and recoverysystem (not illustrated) wherein the acidic anode electrolyte solution104 or the basic cathode electrolyte 108 is utilized to dissolve calciumand/or magnesium-rich minerals e.g., serpentine or olivine, or wastematerials, e.g., fly ash, red mud and the like, to form divalent cationsolutions that may be utilized, e.g., to precipitate carbonates and/orbicarbonates as described herein. In some embodiments, the precipitateddivalent carbonate and/or bicarbonate compounds may be utilized asbuilding materials, e.g., cements and aggregates as described forexample in commonly assigned U.S. patent application Ser. No. 12/126,776filed on May 23, 2008, herein incorporated by reference in its entirety.

In an alternative embodiment, the present system and method areintegrated with an industrial waste gas treatment system (notillustrated) for sequestering carbon dioxide and other constituents ofindustrial waste gases, e.g., sulfur gases, nitrogen oxide gases, metaland particulates, wherein by contacting the flue gas with a solutioncomprising divalent cations and the present cathode electrolytecomprising hydroxide, bicarbonate and/or carbonate ions, divalent cationcarbonates and/or bicarbonates are precipitated as described in commonlyassigned U.S. patent application Ser. No. 12/344,019 filed on Dec. 24,2008, herein incorporated by reference in its entirety. Theprecipitates, comprising, e.g., calcium and/or magnesium carbonates andbicarbonates in some embodiments may be utilized as building materials,e.g., as cements and aggregates, as described in commonly assigned U.S.patent application Ser. No. 12/126,776 filed on May 23, 2008, hereinincorporated by reference in its entirety.

In another embodiment, the present system and method are integrated withan aqueous desalination system (not illustrated) wherein the partiallydesalinated water of the third electrolyte of the present system is usedas feed-water for the desalination system, as described in commonlyassigned U.S. patent application Ser. No. 12/163,205 filed on Jun. 27,2008, herein incorporated by reference in its entirety.

In an alternative embodiment, the present system and method areintegrated with a carbonate and/or bicarbonate solution disposal system(not illustrated) wherein, rather than producing precipitates bycontacting a solution of divalent cations with the first electrolytesolution to form precipitates, the system produces a solution, slurry orsuspension comprising carbonates and/or bicarbonates. In someembodiments, the solution, slurry or suspension is disposed of in alocation where it is held stable for an extended periods of time, e.g.,the solution/slurry/suspension is disposed in an ocean at a depth wherethe temperature and pressure are sufficient to keep the slurry stableindefinitely, as described in U.S. patent application Ser. No.12/344,019 filed on Dec. 24, 2008, herein incorporated by reference inits entirety; or in a subterranean site.

1. An electrochemical system comprising: a cathode electrolytecomprising added carbon dioxide and in contact with a cathode in acathode compartment; a first cation exchange membrane separating thecathode electrolyte from an anode electrolyte wherein the anodeelectrolyte is in contact with an anode in an anode compartment andcomprises a salt and an acid; a mineral dissolution system operativelyconnected to the anode compartment and wherein the mineral dissolutionsystem is configured to dissolve a mineral with the acid in the anodeelectrolyte and produce a mineral solution comprising divalent cations,un-reacted acid and the salt; and a nano-filtration system operativelyconnected to the mineral dissolution system and wherein thenano-filtration system is configured to receive the mineral solution andproduce a first mineral solution comprising the salt and un-reactedacid, and a second mineral solution comprising divalent cations.
 2. Theelectrochemical system of claim 1, comprising a second cation exchangemembrane in contact with the anode and wherein the second cationexchange membrane is configured to separate the anode from the anodeelectrolyte.
 3. The electrochemical system of claim 1, wherein thecarbon dioxide added to the cathode electrolyte is contained in a wastegas from an industrial operation comprising an electrical powergenerating plant, a cement plant, an ore processing facility or afermentation system.
 4. The electrochemical system of claim 3, whereinthe cathode electrolyte is configured to prevent atmospheric carbondioxide from entering into the cathode electrolyte.
 5. Theelectrochemical system of claim 4, wherein the cathode electrolyte isoperatively connected to the industrial facility to receive the wastegas comprising carbon dioxide.
 6. The electrochemical system of claim 5,wherein water is reduced to hydroxide ions and hydrogen gas at thecathode with an applied voltage across the anode and cathode, andwherein hydroxide ions at the cathode are migrated into the cathodeelectrolyte to produce the cathode electrolyte comprising hydroxide ionsand/or bicarbonate ions and/or carbonate ions.
 7. The electrochemicalsystem of claim 6, wherein hydrogen gas is oxidized to hydrogen ions atthe anode and wherein the hydrogen ions are migrated into the anodeelectrolyte to form the acid in the anode electrolyte.
 8. Theelectrochemical system of claim 7, wherein the anode is configured tooxidize hydrogen gas to hydrogen ions and the cathode is configured toproduce hydroxide ions and hydrogen gas with less than 1V applied acrossthe anode and cathode, without producing a gas at the anode.
 9. Anmethod comprising: adding carbon dioxide into a cathode electrolyte incontact with a cathode in a cathode compartment of an electrochemicalsystem wherein the cathode electrolyte is separated from an anodeelectrolyte by a first cation exchange membrane and wherein the anodeelectrolyte is in contact with an anode in an anode compartment;producing an alkaline solution in the cathode electrolyte withoutproducing a gas at the anode in contact with the anode electrolyte byapplying a voltage across the anode and cathode to reduce water tohydroxide ions and hydrogen gas at the cathode, migrate the hydroxideions into the cathode electrolyte, and migrate cations from a salt inthe anode electrolyte into the cathode electrolyte through the firstcation exchange membrane; producing an acid in the anode electrolyte byreducing hydrogen at the anode to hydrogen ions and migrating thehydrogen ions into the anode electrolyte; dissolving a mineral using theanode electrolyte in a mineral dissolution system operatively connectedto the anode compartment to produce a mineral solution comprisingdivalent cations, un-reacted acid and the salt; and separating the saltand un-reacted acid from the mineral solution in a first mineralsolution, and separating the divalent cations from the mineral solutionin a second mineral solution using a nano-filtration system.
 10. Themethod of claim 9 comprising producing hydroxide ions and/or bicarbonateions and/or carbonate ions in the cathode electrolyte.
 11. The method ofclaim 10, wherein the carbon dioxide added to the cathode electrolyte iscontained in a waste gas from an industrial operation comprising anelectrical power generating plant, a cement plant, an ore processingfacility or a fermentation system.
 12. The method of claim 11, whereincarbon dioxide in ambient air is excluded from the cathode electrolyte.13. The method of claim 12, comprising maintaining a pH of between 8 and11 in the cathode electrolyte.
 14. The electrochemical system of claim8, further comprising a reverse osmosis system operatively connected tothe nano-filtration system and wherein the reverse osmosis system isconfigured to concentrate the salt and un-reacted acid in the firstmineral solution to produce the anode electrolyte.
 15. Theelectrochemical system of claim 14, wherein the reverse osmosis systemis operatively connected to the anode compartment and wherein thereverse osmosis system is configured to replenish the anode electrolytein the anode compartment.
 16. The electrochemical system of claim 15,wherein the second mineral solution comprises calcium and/or magnesiumions.
 17. The electrochemical system of claim 16, further comprising acarbonate precipitation system operatively connected to thenano-filtration system and to the cathode compartment, and wherein thecarbonate precipitation system is configured to receive cathodeelectrolyte from the cathode compartment and the second mineral solutionfrom the nano-filtration system, and produce a carbonate and/orbicarbonate by mixing the waste gas with the cathode electrolyte and thesecond mineral solution.
 18. The electrochemical system of claim 17,wherein the carbonate ad/or bicarbonate comprises calcium carbonate,calcium bicarbonate, magnesium carbonate and/or magnesium bicarbonate ora mixture thereof.
 19. The electrochemical system of claim 18, furthercomprising a salt concentrator operatively connected to the anodecompartment and configured to receive the anode electrolyte andconcentrate the salt therein.
 20. The electrochemical system of claim19, wherein the anode comprises a gas diffusion anode.
 21. The method ofclaim 13, comprising isolating the anode from the anode electrolyteusing a second cation exchange membrane and migrating the hydrogen ionsfrom through the second cation exchange membrane into the anodeelectrolyte.
 22. The method of claim 21, comprising concentrating thefirst mineral solution by reverse osmosis to produce a concentratedfirst mineral solution and using the concentrated first mineral solutionas the anode electrolyte.
 23. The method of claim 22, comprising mixingthe cathode electrolyte with the waste gas and the second mineralsolution to produce a carbonate and/or bicarbonate comprising calciumand/or magnesium.
 24. The method of claim 23, comprising withdrawing aportion of the anode electrolyte from the anode compartment,concentrating the withdrawn anode electrolyte by removing water, andreturning the concentrated anode electrolyte to the anode compartment.